@raffy The Restricted Mode setting should not block YouTube entirely. Can you check that you don’t have a calendar that blocks YouTube at the moment?
Some variations you might want to try to pin point the problem:
1. Turn off Restricted Mode and see if the problem goes away.
2. With Restricted Mode on, try youtube.com from a browser on the Android phone. Can you watch YouTube this way? If not, what is the error or warning?